What should I do with my colleague who lives and works with me, who creates problems for me at work, refuses reconciliation, and whose actions and disregard for me cause me psychological suffering?

A Muslim has rights over his Muslim brother. If a Muslim fulfills these rights towards his brother, he has done what is required of him and is considered to be maintaining ties with his brother, not abandoning him. It is advisable to counsel the one who abandons another and remind him of the impermissibility of a Muslim abandoning his brother, and to respond to his ill-treatment with kindness. Allah Almighty says: "And not equal are the good deed and the bad. Repel [evil] with that which is better, and thereupon the one whom between you and him is enmity [will become] as though he was a devoted friend."